MAY 24, 1928
THE BRISTOL " JUPITER" FAMILY (I)
Leading Particulars of Seven Standard Types
IT IS an old saying that imitation is the sincerest form offlattery. In the aero engine world, the modern form of imita-
tion, fortunately, often takes the form of building underlicence, and on this basis probably no aero engine in the world
has been the subject of a greater amount of sincere flatterythan the Bristol " Jupiter," which is being, or about to be,
manufactured under licence in a great number of foreigncountries. Thus, at the present moment, the " Jupiter " is
being manufactured in no less than eleven different countries.This fact speaks for itself. Moreover, the " Jupiter " is in
use in the military and naval services of more than 20 Euro-pean countries, while an ever-increasing number of engines
are being employed in commercial aviation, the recent typeswhich have been added to the " Jupiter " family having been
produced largely with the requirements of civil aviation inview.
The popularity of the Bristol " Jupiter " engine being by
now well established, we have thought it would interest
our readers, both at home and abroad, to have a fuller account
than has hitherto been possible of the number of types now
available, the details of their design and construction ex-
plained and illustrated. We have, therefore, made special
arrangements with the Bristol company in the matter of plac-
ing at the disposal of FLIGHT much detailed information
which has not yet been published, so that our readers will
be the better able to understand the reasons which have
contributed to the favour with which.the " Jupiter " engine
is regarded at home and abroad. One feature of the engine,
of vast importance in itself, which no amount of description
or illustration can adequately convey, is the exquisite work-
manship put into these engines by the Bristol Company. A
tour of inspection of the new engine works at Filton, such as
we were privileged to make recently, leaves one amazed.
Firstly, that it should be possible, and secondly, that it should
be commercially practicable. We have not the space here
to go into details concerning the manufacturing side, but
perhaps some little idea of the degree of care bestowed upon
the manufacture of the Bristol " Jupiter " engines can be
formed when we point out that already a large percentage
of the components from which the engine is made are machined
all over. At the moment this applies to the crankcase, for
instance. It is likely to be extended to even more compli-
cated parts, such as cylinder heads. But the point to keep
in mind is that nothing but the best is regarded at Filton as
being good enough.
It might be argued that such refinement is not really neces-
sary. Mr. Feddon has a good reply to this. His argument
is that, if under peace time conditions something better
than merely good enough is produced, then in case of emer-
gency, when mass production must inevitably reduce quality
to some extent, the engine will still be thoroughly sound and
reliable. It might be thought that such meticulous care
as is taken in the manufacture of the " Jupiter " must resultin a very high price. Actually this does not appear to be
the case. Probably this is due, in no small measure, to thegenius of Mr. Wriitehead, who presides over the engine
works, and who appears to have solved the problem ofcombining laboratory workmanship with quantity production.
One can see directions in which some of the extra cost ofmachining operation may be regained in a saving in scrap
and waste of castings, etc., but even so, the layman is puzzledto reconcile such perfection of workmanship and finish with
a reasonable commercial price. Probably the truth is onewhich Mr. J D. North is fond of expressing somewhat as
follows : " When a critic complains that a thing is expensiveto make, it usually merely means that he does not know hovr
to make it."
However, to return to the family of "Jupiters" nowavailable, since the beginning of the present year the Bristol
company has standardised seven distinct types of engine,of which three are of the direct drive " Jupiter VI " series,
known as the VI.A (compression ratio 6-3 : 1), the VI A.M.(compression ratio 5-3: 1), and the VI A.L. (compression
ratio 5:1). One is a standard service engine with gear-drivensupercharger, and is known as the Series VII. The remaining
three are geared engines fitted with the 2 : 1 Farman reductiongear for which the Bristol company has secured the British
rights, and are designated as Series VIII, IX and XI, respec-tively, according to compression ratio. The VIII is a stan-
dard service engine, with a compression ratio of 5-8:1.The IX is a general purpose engine, with a compression ratio
of 5-3 : 1, and the XI is the commercial version, with a com-pression ratio of 5 : 1.
In the same way, the Series VI consists of a high-compres-sion type, standard service engine, the VI.A., the VI.A.M.
general purpose engine, and the VI A.L. commercial engine.
The main particulars of each type are given in the tablebelow.
It is not intended here to go into details concerning thedesign and construction of the " Jupiters," but a few remarks
may be of assistance in forming an opinion as to the mainfeatures of the different types. To begin with, the " Jupiter "
VIA, is the famous VI with certain detail improvements.For instance, the cylinders and pistons have been improved,
the former having additional cooling fins, triple valve springsand ball-bearing rocker gear. These improvements have
been included in the whole series, making them interchange-able as regards cylinder components. As already stated, the
difference between the Series VI A and the VI A.M. andVI A.L. is one of compression ratio only.
The Series VII " Jupiter " is interesting on account of thefact that it is fitted with a gear-driven supercharger designed
to maintain ground-level power up to 12,000 ft. The gearingand drive for this blower has been the subject of very careful
Leading Particulars of Bristol " Jupiter " Engines
Engine, Series
Bore, inchesStroke, ,,
Swept vol., cub. in.
,, litres
Compression ratio
Normal engine r.p.m.
Gear ratioPropeller
id f Normal r.p.m. of prop.§ J Normal h.p.
g I Max. r.p.m. of prop.
O I Maximum h.t).
T3X)
"S -^ -<«2
<
' Altitude, ft
Normal r.p.m. of prop...
Normal h.p.XT
Max. r.p.m. of prop.Maximum h.t). . .
Icrnition . ....
Oil pressure lb./sq. in . .
Oil return, normal r.p.m., gals./hr. . .
Tachometer drive, fraction of engine speedStandard weight, bare lbs.
Engine control ..
VI A.
5-75
7-501,752
28-7226-3:1
1,700
Nil
L.H.T.1,700
415
'.. 5,000
1,700
415
1,870
460Fixed
40
45
i720
Gate
Throttle
* Gate throttle
VI A.M.
5-75
7-501,752
28-7225-3 : 1
1,700
Nil
L.H.T.1,700
440
1,870
480
Ground
—
——
—Fixed
40
45
i720
Standard
boost gauge
389
VI A.L.
5-757-50
1,752
28-7225 0: 1
1,700
Nil
L.H.T.1,7001
420 1
1,870 f
460 J
Ground
—
—
—
—Fixed
40
45
\
720
Standard
VII
5-757-50
1,752
28-722
5-3 : 1
1,775Nil
L.H.T.
See fPower <
Curve
12,000
1,775
420
1,950
—Fixed
40
40
i760
*
VIII
5-757-50
1,752
28-7225-8 : 1
2,000
2 : 1L.H.T.
1,000
450
3,000
1,000
4551,100
490Fixed
60
65
J880
Gate
Throttle
IX
5-757-50
1,752
28-7225-3 : 1
2,000
2 : 1L.H.T.
1,000485
1,100
525
Ground
—
—
—
—Fixed
60
65
\
880
Standard
XI
5-757-50
1,752
28•722
5-0 : 1
2,0002 : 1
L.H.T.1,000
460
1,100
500
Ground
—
—
—
—Fixed
60
65
88C
Standard